Comparative Life-Cycle Assessment (LCA) of Textile Bleaching Systems:Gentle Power Bleach™ vs. Conventional Bleaching System

Chris Dettore, Genencor, A Danisco Division ABSTRACT

Currently, the textile industry faces major challenges related to resource management. Given ~26

million metric tons of cotton are produced annually, improvements in processing can lead to

significant reductions in the industry “footprint”. Cotton bleaching serves to brighten the color of

fabric and prepare it for further processing. The majority of cotton produced undergoes a conventional

bleaching process. Gentle Power Bleach™ (GPB) is an enzyme-based bleaching system, which allows

bleaching to occur at lower temperatures and with less water. This life-cycle assessment compares the

environmental impacts associated with conventional and GPB for producing cotton fabrics. Results

show a marked advantage for GPB. Relative to conventional, GPB showed at least a 20% benefit in

most impact categories, including climate change, human health, ecosystem quality and water use.

1. INTRODUCTION & OBJECTIVES

• Conventional bleaching techniques require the use of high temperatures and large amounts of chemical

additives (caustic) necessary for modifying and neutralizing pH.

• GPB enables reduced temperature, neutral pH bleaching conditions, through its enzymatic technology.

• Due to differences in composition as well as processing parameters—particularly temperature—these

bleaching systems may have significant differences in their environmental profiles (impacts).

• This comparative environmental life-cycle assessment (LCA) quantifies the potential environmental

impacts associated with conventional bleach and GPB for producing bleached, dyed and softened cotton

fabrics.

• The objectives of this study are to assess whether the use of GPB shows a net environmental benefit

and, if so, to evaluate the magnitude of this benefit by examining the potential environmental impact of

both bleaching systems.

2. ENZYMATIC BLEACHING MECHANISM

• The GPB system utilizes Genencor’s PrimaGreen® EcoWhite liquid enzyme formulation containing a

bacterial arylesterase enzyme.

• This unique proprietary enzyme system designed for textile bleaching catalyzes the perhydrolysis of

propylene glycol diacetate to form propylene glycol and peracetic acid (bleaching agent) in situ at a

neutral pH and over a wide range of temperatures.

• Perhydrolysis is a well documented side activity observed for esterases, however, hydrogen peroxide

competes with water to react with the ester substrate in the catalytic site of these esterases and the rapid

formation of the undesired acetic acid has prevented these enzymes from effective use in textiles

bleaching applications in the past.

• The Genencor enzyme has an unprecedented preference to favor catalysis of the perhydrolysis reaction.

The perhydrolysis vs. hydrolysis ratio of the enzyme has been optimized through protein engineering to

yield an enzyme product enabling effective and commercially viable in situ generation of peracetic acid

under mild aqueous application conditions (low temp and pH).

Figure 1: Arylesterase – substrate ‘in-situ’ mechanism

7. CONCLUSIONS

Figure 2: Cotton fabric treated via enzymatic bleaching

4. SYSTEM DETAILS

Figure 5: System boundaries of cotton bleaching systems

Additional system details

• As the unit of analysis, 1 kg of treated cotton fabric was selected to be the “functional unit” for this study.

• The current market situation has been evaluated to provide an accurate reflection of production locations (cotton fiber, yarn, fabric, treatment

chemicals, bleaching solution), the use of various technologies, process efficiencies and transport modes and distances within the production

chain.

• Assumed:

• Cotton production: 60% in Asia, 40% in the Americas

• Weaving of cotton fabric: 70% in Asia, 30% in Europe

• Cotton treatment occurs in many countries, influencing transportation distances from the site of bleaching solution preparation to the site of

cotton treatment. Identified production locations and market distribution patterns were used to model the transportation of the bleach solution

inputs (chemicals, enzymes) to the production location and the bleaching solution to the location of treatment.

• This study is conducted to be generally applicable to global markets for the cotton fabrics in question and to represent present conditions.

This has been achieved through the use of the most current information that could be obtained at the time of the launch of the study and by

basing all processing on a weighted average of conditions occurring among the major cotton production and treatment geographies.

Boundaries of cotton bleaching systems

3. METHODS: Life-Cycle Assessment (LCA)

What is LCA?

• Defined by the ISO Standard (14040)as:

“ a careful compilation and evaluation

of the inputs, outputs and the potential

environmental impacts of a product

system throughout its life cycle”

• A systematic methodology that

establishes an environmental “profile”

of the product/system.

Figure 3: Life-cycle inventory stage of LCA Figure 4: Life-cycle impact assessment stage of LCA

Life-Cycle Inventory

• Transportation included between life-cycle stages

Life-Cycle Impact Assessment

Key system differences:

5. RESULTS – Climate Change Impact• Calculated using the “Impact 2002+” impact assessment method based on the IPCC 100 year GWPs

6. RESULTS – Additional Impact Categories• Calculated using the “Impact 2002+” impact assessment method

• The overall benefit of the GPB system is ~5% relative to the standard bleaching

system.

• The production of the cotton fabric accounts for greater than 80% of the potential

impacts for both the GPB and standard bleaching system.

• While the mass of cotton lost during the bleaching process differs between the

two systems, the cotton that remains in the final product is the same (1kg). As

such, it is revealing to view the results omitting the production of the 1 kg cotton

fabric (but including the cotton lost during bleaching).

• The red outline illustrates the results of the comparison when 1 kg cotton fabric is

omitted. Figures 7-9 display results within the red outline.

• The magnitude of the difference between systems appears more substantial .

Overall benefit for GPB here is ~20%

• The GPB system provides a benefit for some life-cycle stages, and a greater

impact for others.

• The major benefit is associated with the reduction in cotton lost during

bleaching, while the production of the bleaching solution presents higher climate

change impacts relative to the equivalent stage for the standard system.

• The additional impacts of the GPB system are more than offset by the reduction

in cotton loss (i.e. less cotton production required to fulfill functional unit 1 kg of

treated cotton fabric) and in the energy efficiencies gained during bleaching and

rinsing (i.e. reduction in treatment temperature and number of rinses translates

into reductions in energy required to heat water).

• As shown in Figure 7, the impact of producing the

bleaching solution is greater for the GPB system. This can

be attributed to the components Invatex LTA (PGDA),

peroxide, peroxide killing (catalase enzyme) and Invazyme

LTE (arylesterase enzyme).

• Impacts from transportation of inputs is also higher for

the GPB system.

• These are more than offset by the improvements in

process efficiency (“heating”) and reductions in cotton loss

(“cotton fabric”).

• In addition, several component of the standard system

show higher impacts (NaOH, neutralizing agent).

Figure 6: Climate change impacts by system

Figure 7: Climate change impacts by system (omitting 1 kg cotton fabric production)

Figure 8: Climate change impacts by component

Figure 9: Comparison of bleaching systems among other indicators

Figure 10: Contributions to the environmental benefits achieved by GPB

Figure 11: Potential annual benefits (reductions) of broad application of GPB system

• A benefit is seen for the GPB system in all impact categories.

• The general trend seen for the two for climate change impacts holds when considering the additional

impact categories (~20% benefit), with several exceptions:

• For “Resource Depletion” the benefit is reduced to ~10%

• For “Ecosystem Quality” and “Water Use, Non-turbined” the benefit is

increased to ~30%.

• The benefits achieved by GPB are split between those occurring from the reduction in cotton loss,

which contributes the majority to human health, ecosystem quality and non-turbined water use and

those from the efficiency of treatment processes, which contribute a majority to resource depletion

and turbined water use.

• Climate change benefits are contributed to equally by the two aspects mentioned above.

• The bars represent the magnitude of total difference in impacts between the two bleaching

systems. Left of 0% represents additional impacts attributed to the GPB system. Right of 0%

represents benefits attributed to GPB.

• GPB positively shifts the total potential impacts in all impact categories, relative to the

standard bleaching system.

• Relative to the standard system, greater impacts are seen from the GPB in the production of

the bleaching solution, and the transportation of the chemical inputs and the bleaching

solution itself.

• The benefits of GPB more than offset the additional impacts, and can be attributed to

reduction in cotton loss (“cotton fabric production”) and “cotton fabric treatment” (i.e.

efficiencies gained during bleaching/rinsing).

• Considering that ~26 million metric tons of cotton fabric are produced annually, most of which is

treated with processes similar to the conventional methods examined in this study, it provides a

perspective on the potential improvement in environmental performance offered by large scale

adoption of an enzyme-based bleaching alternative, such as GPB.

• For the impacts in question by such large shifts in an industry, it is useful to compare the results

with quantities or benchmarks that may be easier to visualize or comprehend than standard metrics

such as kilograms of carbon dioxide equivalents.

• Here we see the potential benefits of switching 26 million metric tons of cotton production from

conventional bleaching to the GPB system.

• For example, switching to GPB would yield reductions in turbined water use >2x the volume of the

Hoover Dam reservoir. Reductions in climate change impacts would be nearly equal to the annual

emission from 7 coal fired power plants.

• A life-cycle assessment has been conducted to compare conventional and Gentle Power Bleach™ systems for

producing treated cotton fabric.

• The study shows that the production of cotton fabric is the most important contributor to environmental

impacts for each system., with the bleaching, dyeing and softening processes contributing only as much as 10-

20% of the total impacts.

• Although treatment processes are a minor contributor to the total impact of treated cotton fabric, it is here

that the differences are revealed for the systems being compared.

• It is found that an environmental advantage exists for the switch from conventional bleaching to the GPB

system. While the advantage is clear under typical market conditions, each value chain might assess their

own unique conditions and consider more specifically the level of benefit they may experience, which is likely

to vary with such factors as geography, technology and the cotton characteristics.

Product Life Cycle

Inventory

Raw Material

ExtractionProduction

Product Use

Product End of Life

Resources ResourcesResourcesResources

EmissionsEmissionsEmissions EmissionsHuman toxicityRespiratory effectsOzone layer depletion, etc.

Human Health

Ecosystem Quality

Resource Consumption

Climate Change• CO2, Nox, CH4

• Crude Oil• Iron ore• Phosphates• Hundreds more…

Water Use

Terrestrial/aquatic ecotoxicityAcidification, EutrophicationLand occupation

Mineral ExtractionNon-renewable energy

GHG Emissions

Freshwater withdrawalOther water uses

ACKNOWLEDGEMENTS

• I would like to thank Quantis International, consultants, for their integral role in completing this LCA study.• Huntsman, Genencor, Primagreen and ISO are registered trademarks. Gentle Power Bleach is a trademark of Huntsman Corp.